Apparatus for painting and baking an article

ABSTRACT

AN IMPROVED APPARATUS FOR SPRAY PAINTING AN ARTICLE AND BAKING THE PAINT IS DISCLOSED. THE ARTICLEWHILE SUPPORTEDON A GRILLE PLATFORM IN A SUBSTANTIALLY AIRTIGHT BOOTH IS FIRST SPRAY PAINTED WHILE MAINTAINING A FLOW OF FRESH FILTERED AIR DOWNWARDLY WHICH MAINTAINING A FLOW OF A FLOWING WATER SCREEN BEFORE BEING EXHAUSTED FROM THE BOOTH. DURING THE BAKING STEP, THE AIR IS RECIRCULATED AND HEATED.

APPARATUS FOR PAINTING AND BAKING AN ARTICLE Original Filed May 1.8, 1965 P. FULFORD Feb. 9, 1971 2 Sheets-Sheet 1 In uew 7012 7 112.!

A-rromn avs Feb. 9, 1971 p FULFORD I 3,561,135

7 APPARATUS FOR PAINTING AND BAKING AN ARTICLE Original Filed May 18. 1965 2 Sheets-Sheet 2 INvENT R 2. 22 E Yflr J 'B M m 012, qrl'n b afs n ATTORNEYS United States Patent 3,561,135 APPARATUS FOR PAINTING AND BAKING AN ARTICLE Peter Fulford, 13 Liverpool Road, Kingston-on-Thames, Surrey, England Continuation of application Ser. No. 456,635, May 18,

1965. This application Nov. 18, 1968, Ser. No. 778,008 Int. Cl. F26b 19/00, 25/06 US. Cl. 34-224 Claims ABSTRACT OF THE DISCLOSURE This application is a continuation of my copending application, Ser. No. 456,635, filed May 18, 1965, and now abandoned.

The invention relates to an improved method of painting and baking an article and to apparatus for carrying out said method. The method and apparatus of the invention are particularly suitable when low temperature bake enamel is employed and a good finish is required and it is desired to perform the operations of paint spraying and baking within the same enclosure or booth, without necesarily moving the article. The painting of articles such as motor vehicles, after they have been in use, presents difiiculties arising from the fact that the under part of the vehicle may be in a dirty condition. Dirt may drop from the vehicle during the spraying or baking process, and subsequently contaminate the finish. Also, since the baking process necessitates recirculation of the air inside the booth, it is essential that spray dust from the spray proces shall have been withdrawn and at least not allowed to settle on the booth floor, so that it cannot be carried into the recirculation duct back to the air heater for reentry.

An object of the invention is to provide a method and apparatus by which the atmosphere in the booth in which an article is to be painted and baked can be more readily and effectively kept clean so as to avoid contamination of the finish.

According to the invention, a method of painting an article comprises placing the article in a closed booth, maintaining a downward flow of clean air over the article and a flow of liquid over at least an area of the booth floor beneath the article whilst it is being painted, stopping said flow of liquid at the end of the painting operation, and then filtering and recirculating the air from the booth through a heater while maintaining the downward air flow in the booth, to dry the paint.

The air is preferably fed into the top of the booth and extracted at or near the floor level thereof. The flows of air entering and leaving the booth are preferably so related as to maintain a pressurised condition within the booth.

Acording to a further feature of the invention, the air extracted from the booth during the painting operation is drawn through a screen of liquid. In this way, combustible materials such as spray dust or pigments can be elfectively filtered out of the air before it is discharged into the atmosphere.

Apparatus for carrying out the method according to the 3,561,135 Patented Feb. 9, 1971 ice invention comprises an enclosed booth, a grille platform near the bottom of the booth for supporting an article in the booth, means for maintaining a flow of liquid over at least an area of the booth floor beneath said grille,

5 means for introducing clean air into the top of the booth and for extracting air from below the said grille during the painting operation, and means for filtering, heating and recirculating the air supplied to the booth during the baking operation.

The apparatus has the advantage that both the painting and baking operation can be conducted in a single booth without removal of the article being treated therefrom. A further advantage resides in the fact that no excavation of the ground below the booth is necessary.

A preferred apparatus for carrying out the invention and suitable for the spray painting of motor vehicles will now be described in more detail by way of example and with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic sectional elevation through the lower part of a spraying booth,

FIG. 2 is a diagrammatic transverse section through the booth showing the air circulation during the baking operation,

FIG. 3 is a diagrammatic transverse section through the booth showing the air circulation during the paint spraying operation,

FIG. 4 is an end elevation of the spraying booth,

FIG. 5 is a perspective view illustrating the water ciroulation,

FIG. 6 is a fragmentary sectional view taken on the line VIVI of FIG. 1.

The apparatus comprises a booth 10 for receiving a vehicle (whose outline is shown diagrammatically at 11 in FIGS. 2 and 3) and having doors 6 capable of being closed with the vehicle therein so as to render the booth substantially airtight.

The booth is provided near its base 12 with a grille platform 13 for supporting the vehicle 11 to be painted. This grille 13 is spaced above the base 12 of the booth so that the necessary drainage and air extractor ducts can be arranged beneath it, as described below, without necessitating excavation below the surrounding floor level. A ramp 5 (FIGS. 4 and 5) is provided to allow vehicles to be driven on to the grille 13.

The roof 14 of the booth is provided with a duct 15 extending substantially along the length thereof. The underside of the duct 15 comprises a series of air filter panels 15a (FIG. 5) through which air can be impelleo from the duct 15 into the booth 10. Air is supplied to the duct 15 from an air heater and fan unit 8. The booth is provided beneath the grille 13 with two air exhaust ducts 16 extending from end to end of the booth and connected to a fan or fans (not shown) arranged to extract air* from the booth during the painting operation and to discharge it to the atmosphere. Preferably the capacity of the fans and ducts for impelling air into the booth is slightly greater than those for extracting air from the booth, so that the interior of the booth can be maintained slightly above atmospheric pressure.

A recirculating air duct 7 having a longitudinal inlet provided with filter panels 9 is disposed between and parallel to the exhaust ducts 16. Its outlet is connected to the inlet of the air heater and fan unit 8. The latter unit also has a fresh air inlet 4, and a flow damper 3 which can be set so that the unit either draws fresh air from the atmosphere (as shown in FIG. 5) or draws recirculated air from the duct 7, and delivers it to the duct 15.

The grille 13 consists of sections supported through inverted channels 13a on square-section transverse tubes 13b (see FIGS. 1 and 6') and is spaced slightly above a series of flat trays 17 which present a substantially continuous surface over the area beneath the grille 13. Mounted along the centre line of the booth immediately above the trays 17 is a pair of water distribution pipes 18 each having a series of lateral outlets 19 for distributing a layer of water over the entire surface of the respective trays 17. A third tray 20 is located along the centre line of the booth 10 above the Water distribution pipes 18, While the trays 17 are disposed on each side of the centre line and extend substantially to the sides 21 of the booth 10. The side trays 17 are slightly inclined downwardly towards the sides 21 of the booth so that water falling thereon from the pipes 18 flows down the trays and is directed into troughs 22 located under the lower edges of the respective trays 17 Transverse channel-shaped baffles 23 secured to the underside of the tubes 13b and to the walls 21 define transverse air passage 23a leading to the air exhaust ducts 16. The air passages 23a are thus arranged so that the air extracted from the booth is drawn through a screen of water as the latter falls from the lower edges of the side trays 17 into the collecting troughs 22, as shown by the arrows 24 (FIGS. 1 and 3). The air is scrubbed as it passes through the passages 23a over the water in the troughs 22, by the action of scrubbing baffles 22a. As a result, combustible materials such as suspended pigments (spray dust) are effectively filtered out of the air extracted from the booth, which can therefore safely be discharged into the atmosphere. No spray dust can collect on the floor because the fiow of water over the trays 17 washes it away. Further, the fact that combustible materials are washed off the floor and out of the air means that no combustible deposits can build up and it is possible to use direct gas-fired air heating in the unit 8 with safety.

The water falling into the troughs 22 is withdrawn from the booth and recirculated by means of a motordriven centrifugal pump 25 (FIG. which draws the water from the troughs 22 through filters 27 and pipes 26 and delivers it to the distribution pipes 18, so that only clean water enters the booth.

During the spraying period, in which the vehicle 11 in the booth is being sprayed with a low temperature bake paint by means of a spray gun handled by an operator within the booth, the damper 3 of the air heater and fan unit 8 is adjusted to draw in 100% fresh air. The unit '8 heats the air to approximately 70 F. and circulates it downwardly as shown in FIG. 3, while water flows over the trays 17 as shown in FIG. 1.

Owing to the comparatively high velocity of the air flow through the fresh air intake 4 during the spraying operation, it is difficult to prevent a certain amount of air from being drawn into the unit 8 from the recirculation duct 7 by leakage around the damper 3. Such air, if drawn from the booth 10, would be likely to contain suspended spray dust which would contaminate the finish. To avoid this, a damper-controlled bypass duct (not shown) is provided in the air heater and fan unit 8, which bleeds off a small proportion of air from the output side of the unit 8 and delivers it to the recirculating duct 7 during the spraying operation. This ensures that no dustladen air from the booth 10 can flow through the recirculating duct 7 during the spraying operation.

After the spraying operation is completed, the water flow is stopped and the operator leaves the booth. The air flow is continued for about ten minutes to evaporate the greater part of the paint solvent.

For the subsequent baking operation, the damper 3 of the unit 8 is moved into its other position, in which only about 10% of the air intake is drawn through the fresh air inlet 4. The remainder of the air intake is air extracted from the booth 10 through the filter 9 and the recirculating duct 7. The circulation in the booth is as shown in FIG. 2. The fan (not shown) which exhausts to atmosphere through the ducts 16 is fitted with a flow damper which during this part of the operation is adjusted to reduce its intake to about 10% of normal. The recirculating air is extracted from the booth through the spaces below and on either side of the central tray 20 as shown by the arrows 30 in FIGS. 1 and 2. During recirculation the heater is adjusted to produce a temperature rise of the air passing through the unit 8 of approximately 40 F. The temperature of the air in the booth gradually rises to about 200 F. The circulation is maintained until the paint is sufficiently hardened for the vehicle to be removed.

For safety purposes, a vane (not shown) which actuates a limit switch is mounted in the heater and fan unit 8 so that a necessary air flow is assured before the heater will operate. This is supplemented by a negative pressure switch inside the heater which also must be satisfied that there is a pressure drop which indicates an air flow before the heater will operate.

A vane (not shown) which actuates a limit switch is also situated in one or both exhaust ducts 16, so that should an exhaust not be effected or fan failure occur, the heater will cut outon either the spray or baking cycle. Further to this, an independent electrical thermostat is also located in the heater fan casing. If the air temperature exceeds about 220 F. the thermostat will cut out the heater.

The duct 15 in the roof of the booth may be lightly constructed so as to provide explosion relief.

What I claim is:

1. Apparatus for painting an article with a low temperature bake paint, comprising a closed booth, a grlile platform for supporting the article in the booth, at least one inclined tray located beneath the grille platform, means for maintaining a flow of liquid over the surface of the inclined tray to form a screen of said liquid falling from the lower edge thereof, an air inlet incorporating an air filter in the top of the booth, a first air outlet near the floor level of the booth and adapted to extract air from the booth through said screen of liquid, means for discharging to the atmosphere air extracted from said first air outlet, a second air outlet near the floor of the booth and adapted to extract air from the booth without passing through said screen of liquid and air heater and fan means to supply heated air to said air inlet and filter, said air heater and fan means having an inlet connected to both a source of fresh air and to said second air outlet from the booth, whereby fresh air may be supplied to the booth during application of paint and said air may be heated and recirculated during the baking of the paint.

2. Apparatuus according to claim 1 wherein a pair of trays is provided below the grille, said trays being disposed on opposite sides of the center of said booth and being inclined slightly downwards from the center of the booth to the side thereof, said means for maintaining a flow of liquid comprising at least one distribution pipe for supplying liquid to flow over the upper surfaces of the trays, and the first air outlet comprising at least one air exhaust duct disposed between and parallel to the water troughs with air inlets so directed as to draw air through the screen of falling liquid, said apparatus further comprising a pair of troughs disposed one beneath the lower edge of each tray to receive the liquid flowing thereover, conduit means including filter means leading from said troughs to said distribution pipe and a pump for drawing liquid from the troughs through said conduit means and filter means to the water distribution pipe.

3. Apparatus according to claim 2 wherein the second air outlet is disposed just above the grille platform and extends along the center of the booth.

4. Apparatus according to claim 1 wherein the air inlet comprises a duct extending along the top center of the booth.

5. Apparatus according to claim 4 wherein said duct is adapted to provide explosion relief.

(References on following page) 6 References Cited Engineering Chemistry, vol. 33, N0. 2, February 1941, pp.

230-233. N UNITED STATES FATE TS Gas Journal: Giant Spray Booths Equipped With 2,347,936 5/ 1944 CTeWFOH 34219 Gas, vol. 299, N0. 5007, Aug. 19, 1959, 191.

g t't 117 119 8X 5 Heating Piping and Air Conditioning: Makeup Air 1 enne Heaters, vol. 36, Se t ber 1964, 112 d 11 2,086,514 7/1937 Saunders et al. p cm Pp an 3 2,545,672 3/1951 f DAVID KLEIN, Primary Examiner 2,627,838 2/1953 Hugglns 117119.8X

US. Cl. XJR. OTHER REFERENCES 10 117--102, 119.8; 118-326 Saunders, S. 6.: Paint Recovery, pub. in Industrial and 

